1. Field of the Invention
This invention relates to technology of expanding the capacity of a logical volume.
2. Description of the Related Art
As a method for expanding the capacity of a logical volume, there is known a method disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-15915. In this unexamined application discloses a method in which when the volume capacity is insufficient due to writing from a host computer, a storage system dynamically adds an unused storage area of a physical disk to a segment of a logical volume.
A logical volume used in a host computer is made redundant in order to enhance the safety of the data. Hereinafter, a logical volume used in a host computer is referred to as “original volume” and a logical volume obtained from a redundant original volume is referred to as “replication volume”. There is a case in which a replication volume exists in a storage system where an original volume exists, and there is also a case in which a replication volume exists in a different storage system. In the former case, the replication volume is a copy obtained in the storage system, and in the latter case the replication volume is a so-called remote copy created from a storage system to other storage system.
By associating a replication volume with an original volume, a logical volume cascade (“volume cascade” hereinafter) is created. By associating a replication volume to other replication volume, a longer volume cascade is created, making the original volume redundant. After new data is written to an original volume, the data is copied to the replication volume associated with the original volume. If other replication volume is associated with this replication volume, the data which is copied to this replication volume is further copied to the abovementioned other replication volume. In this manner, the data is copied from an upstream logical volume to a downstream logical volume in a volume cascade.
Therefore, when, for example, the capacity of the upstream logical volume is expanded, it is necessary to expand the capacity of the downstream logical volume so that all data items stored in the upstream logical volume in the downstream logical volume as well. However, a technology for expanding the capacity of a downstream logical volume in response to the expansion of the capacity of the upstream logical volume is not known in a prior art.